Method of producing a transducer



y 1968 F, E. GIFFORD ETAL 3,383,759

METHOD OF PRODUCING A TRANSDUCER Filed Feb. 18, 1966 United States Patent 3,383,759 METHOD OF PRODUCING A TRANSDUCER Fay E. Gifford, Lathrup Village, and Charles W. Williams,

Essexville, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Feb. 18, 1966, Ser. No. 528,564 8 Claims. (Cl. 29-603) This invention relates to a method of forming a ceramic body having a thin metal strip therein, and more particularly to a method for filling a narrow groove in a ceramic body such as a transducer and the like with metal.

Certain devices have a structure including a ceramic body having a thin continuous strip or ribbon of a metal positioned snugly in a narrow slit or groove in the ceramic body. A transducer used to evaluate the high pressure characteristics of lubricants by means of converting mechanical energy into electrical energy is such a device. When a certain force, for example, a rolling contact bearing element, is exerted against the metal strip in the transducer body, the force generates an electrical impulse in the metal strip which may be measured by a galvanometer-type device. A lubricant applied as a coating to the metal strip changes the magnitude of the electrical impulse. The electrical reading on the galvanometer provides a means to evaluate the high pressure characteristics of the lubricants being tested. The metal strip used in the transducer application described above must have a certain electrical resistance in order for the transducer to have the proper sensitivity. In addition, the metal strip must fill the groove completely so that no voids exist. Filling the groove completely so that no voids exist is accomplished by bonding the metal to the walls and the bottom of the groove in the ceramic body.

Bonding a strip of a metal to the outer surface of a ceramic body at elevated temperatures by applying pressure to melted or molten metal thereby producing a close adaptation of the metal to the ceramic surface is well known. However, this method produces a metal strip in the groove having void space-s therein due to the inability of the gases to escape from the molten metal in the groove. Another well known method of forming a tight metal-to-ceramic bond involves painting a ceramic body with a metal powder ink and subsequently heating the ceramic body at an elevated temperature. This method is not satisfactory for narrow grooves due to the inability of the ink to fill the bottom of the groove thereby resulting in a metal strip which contains voids. Moreover, using the metal ink method would require more than one application of the metal ink in order to obtain a metal strip surface which is flush with the adjacent ceramic body surface. These prior art methods are especially unsatisfactory in forming a thin metal strip in a groove of a cylindrical ceramic transducer when the dimensions of the groove are of the magnitude of mills or less in width and 2 mils or more in depth.

It is an object of this invention to provide a method for filling a narrow groove in a ceramic body such as a transducer body and the like with a metal in a manner such as to completely fill the narrow groove to form a continuous void-free metal strip.

These and other objects are accomplished by a method which includes the steps of cleaning thoroughly the narrow groove in the ceramic body. The ceramic body is then dried and degassed. Then metal foil, preferably in the form of a plurality of layers of two or more different metals, is placed over the narrow groove in the ceramic body. The metal foil is lightly clamped to the ceramic body to keep the metal foil directly over the groove. Next, the ceramic body and metal foil are heated in a vacuum to a temperature which causes the metal foil to melt and flow by the force of gravity into the groove. The ceramic body is then cooled and the excess metal protruding out of the groove is ground away.

Other objects and advantages of this invention will be apparent from the following detailed description, reference being made to the accompanying drawings wherein a preferred embodiment of this invention is shown.

In the drawings:

FIGURE 1 is a perspective view of a transducer assembly made in accordance with the present invention;

FIGURE 2 is a perspective view of the transducer assembly prior to the heating step; and

FIGURE 3 is an exploded fragmentary cross sectional view of FIGURE 2 taken at the end of the groove.

Referring now to the drawings, FIGURE 1 shows a transducer assembly 10 made in accordance with the process of this invention having a thin metal strip 12 completely filling the narrow groove 14 which longitudinally traverses the raised portion of the cylindrical ceramic body 16. The upper surface of the metal strip 12 is flush with the surface of the ceramic adjacent to the sides of the metal strip. One end of the platinum wire 18- is embedded at one end of the metal strip 12 and the other end of the platinum wire 18 is connected to electrical lead 22. Similarly, one end of platinum wire 20 is embedded in the other end of the metal strip 12 and the other end of the platinum wire 20 is connected to electrical lead 24.

The process of this invention involves first cutting a narrow groove having a width of the order of less than 0.010 inch and a depth of the order 0.002 inch or more longitudinally in the surface of a raised portion of the cylindrical ceramic body by means of a steel saw blade. The narrow groove is then cleaned by immersing the ceramic body in a series of cleaning solutions and subjecting the ceramic body to ultrasonic vibrations. The ceramic body is dried by heating the body in an oven and degassed by heating the body in a vacuum. Metal foil is placed over the top of the groove whereby the metal traverses and covers the groove and rests on the ceramic surface on each side of the groove. The metal foil is held and lightly clamped in place by a rectangular ceramic strip positioned on top of the metal foil. The ceramic strip is held in place by means of wire strapped around the ceramic strip and the ceramic body. Platinum wires are inserted a short distance into each end of the groove. The two platinum wires are held in place by means of Wire strapped around the platinum wire and portions of. the ceramic body having a reduced diameter. The as sembly thus described is then heated in a vacuum oven to a temperature which causes the metal foil to melt and flow by the force of gravity into and completely fill the groove. After the ceramic body is cooled, the excess metal protruding out of the groove is ground away. An electrical lead is then connected to the free end of each of the platinum wires, the other end of the platinum wires being embedded in the ends of the metal strip in the groove thereby providin a path for an electrical impulse which is generated in the metal strip.

The process of this invention will now be described in greater detail. in reference to FIGURE 2. The ceramic body 16 having the required shape is formed by conventional techniques. An alumina body fired above 1600 C. is the preferred fired ceramic although other suitable ceramics such as beryllium oxide, mullite, zirconium oxide, and the like may be used.

The groove 14 in the ceramic body 16 as shown in FIGURE 3 is formed by sawing the ceramic body with a steel blade. As the width of the groove 14 in the ceramic body 16 is made narrower, the groove is more difficult to fill with a metal strip. This is also true as the depth of the groove is made deeper. It is especially difficult to fill a metal strip in the groove in a ceramic body when the width of the groove is less than 0.010 inch and the depth is 0.002 inch or more. The groove 14 in the preferred embodiment is 0.001 inch wide, 0.002 inch deep and 0.75 inch long. The groove 14 must be cleaned thoroughly to remove dirt, cooling liquids and debris particles that are present as a result of grinding operations. The groove is cleaned by conventional ceramic cleaning methods which include immersing the ceramic body 16 in a trichloroethylene bath and subjecting the ceramic body 16 to ultrasonic vibrations for 30 minutes. The ceramic body 16 is then placed in an aqueous solution of an abrasive cleaner such as hydrated monocalcium phosphate and the like and cleaned using an ultrasonic vibrator for 90 minutes. The ceramic body 16 is there immersed in clean water and subjeted to ultrasonic vibrations for 30 minutes. Thereafter the ceramic body is removed from the water and dried. After drying, the groove is inspected under a miscroscope to see if any ceramic particles, dirt or other debris are present. If any debris is present, the cleaning steps using the abrasive solution and the clean water are repeated. After the groove 14 is clean, water vapor is removed from the ceramic body 16 by firing the body 16 in air at 1000 F. for 20 hours. It is necessary to remove undesirable gases such as oxygen, carbon monoxide or carbon dioxide from the ceramic body 16 in order to prevent these gases from contaminating the groove 14 and metal strip 12 during its formation in the groove. The ceramic body 16 is degassed by firing the body 16 at 1300 C. in a vacuum having a pressure less than 2 10- millimeters of mercury. This degassing operation takes between 30 and 90 minutes.

The metal strip 12 composition should be such that it will form a very tight bond to the ceramic, that is a cermet-type bond. Certain metal alloys are well known to form effective cermet-type bonds with ceramics. These metal alloys, however, are not presently available in the form of a thin sheet or ribbon, the form the metal must be in for this invention. Since these metal alloys are not presently available in foil form, it is necessary to use a plurality of metal foil layers of at least two different metals positioned on top of each other. FIGURE 3 is an exploded end view which shows a plurality of nickel foil 26 and zirconium foil 28 layers. Other metal alloys in addition to the nickel-zirconium alloy used in the preferred embodiment, which are known in the art to form cermettype bonds are nickel-titanium, nickel-molybdenum, nickel-vanadium, nickel-copper, molybdenum-manganese and zirconium-vanadium. The metals preferred in this invention are nickel, zirconium, titanium, vanadium, molybdenum and copper since they are presently available in foil form. Although molybdenum-manganese alloys are well known to form a tight metal-to-ceramic bond, they are not preferred in this invention due to the difficulty of obtaining manganese in foil form. The quantities of the individual metal foils used should be such that the resultant composition of the melted foils which forms the metal strip would be that of an alloy melting at the proper temperature. The proper temperature for the metal foils to melt at would be a temperature approximately 200 or more lower than the firing temperature of the ceramic in order to avoid distortion of the ceramic body. For example, in the case of alumina ceramic which is fired at 1600", a temperature of 1400 C. or lower should be used to melt the metal foils, the preferred temperature range at which these metal alloys should melt is between 950 C. and 1350 C. for ceramics melting in the vicinity of 1600 C. Higher temperatures may be used if the ceramic has a correspondingly higher firing temperature.

The metal foils are cleaned by conventional metal cleaning operations by ultrasonically vibrating the metal parts in an acetone bath for 30 minutes, a trichloroethylene bath for 90 minutes and an ethyl-alcohol bath for 30 minutes. Clean nylon gloves should be worn when handling the metal foils as well as the ceramic parts. Metal foils are subjected to additional processing to improve the brazing results unless the additional processing tends to cause oxidation of the metal as is the case with zirconium or if it tends to destroy the ductility as is the case with molybdenum. Nickel is processed by hydrogen firing at 1000 C. for 30 minutes and followed by a vacuum firing at 1000 C. until the pressure is below 1 10 millimeters of mercury.

The two metal foils should be folded several times to form a narrow strip and then positioned over the narrow groove so that it overlaps the edges of the groove as shown in FIGURE 3. A ceramic strip 30 is placed on top of the metal foil strip so that the ceramic strip overlaps the metal foil strip. The ceramic strip 30 is clamped to the raised portion of the ceramic by tying several pieces of molybdenum wire 32 around the body 16 and ceramic strip 30 as shown in FIGURE 2. The purpose of the ceramic strip 30 and the molybdenum wires 32 are to keep the foil positioned above the narrow groove. Platinum wires 18 and 20 are inserted into the ends of the groove. The platinum wires 18 and 20 are tied to portions of the ceramic body 16 having a reduced diameter with molybdenum wires 34 to maintain their relative position in the assembly.

The assembly described above and as shown in FIG- URE 3 is positioned in a vacuum oven. The pressure in the oven is reduced to l 10 millimeters of mercury and the temperature is raised to a temperature between 950 C. and 1350 C. in the case of zirconium-nickel metal foils. The flowing temperature or melting point of the multilayer metal foil strip varies depending upon the relative weight ratio between the two metal foils used as well as how well the metals are in contact with each other. The relative weight ratio should be selected by referring to the phase diagram of metal system being used, the phase diagram indicating the melting point of any alloy in that system. Since metal foils which are not in good contact with each other melt at a higher temperature than indicated by the phase diagram for that alloy, care must be exercised to insure good contact between the metal foil layers. As mentioned earlier, the temperature of the brazing should be kept at least 200 C. below the firing temperature of the ceramic in order to avoid any distortion of the ceramic body. After the metal foils have melted and filled the groove, the temperature is reduced at a rate of C. per minute until a temperature of 800 C. is reached, at which time the oven is turned off. After the assembly is cooled, the excess metal protruding out of the narrow groove is ground away and the electrical leads 22 and 24, are connected to the exposed ends of the platinum wires 18 and 20.

In a specific illustration of the invention, an alumina ceramic body is fired at 1600 C. A narrow groove of 0.001 inch wide and 0.002 inch deep is cut in the ceramic body with a high speed steel blade. The ceramic body is then cleaned and degassed. A piece of nickel foil /2 inch wide by 1 inch long by 0.001 inch thick weighing 0.004 gram is cleaned by conventional metal cleaning methods and then subjected to firing in a hydrogen atmosphere at 1000 C. for 30 minutes and followed by a vacuum firing at 1000 C. until the pressure is below 1 10- millimeters of mercury. A piece of zirconium foil inch wide by 1 inch long by 0.001 inch thick weighing 0.015 gram is cleaned. The nickel foil is then folded over the zirconium foil so that the zirconium foil is completely covered by the nickel foil on the two sides of the foil. The nickel foil is folded about the zirconium-nickel in order to protect the zirconium from being oxidized, since it is well known that zirconium is readily oxidized. The zirconium-nickel foil lamination is trimmed to of an inch wide by inch long with the fold remaining. The lamination is then folded again so that there are two zirconium and four nickel layers in the foil lamination.

An alumina ceramic strip /s inch by Ms inch by 4 inch long is positioned on top of the zirconium-nickel metal foil lamination. Platinum wires are inserted a short distance into each end of the groove to make contact with the metal after the metal has melted into the groove. The ceramic strip is tied to the ceramic body with molybdenum wire. The assembly thus formed is positioned in a vacuum oven and evacuated to a pressure less than 1 l0 millimeters. The temperature is increased to 1200 C. and held at that temperature while the metal foil melts and fiowssinto the narrow groove. The temperature is raised 30 C. and held for 1 minute. The temperature is then reduced to 800 C. at which time the oven is turned oft". When the assembly is cool, the excess nickel-zirconium protruding out of the narrow groove is ground oli to form a transducer which is ready to be installed.

While the invention has been described in terms of preferred embodiments, it is to be understood that the scope of the invention is not limited thereby except as defined in the following claims.

What is claimed is:

1. A method for filling a narrow groove in a ceramic body such as in a transducer assembly and the like with a metal to form a continuous void-free metal strip com prising the steps of placing metal foil composite on said body whereby said foil composite completely covers the top of said groove, clamping said foil composite to said ceramic body with sufiicient pressure to keep the foil composite from moving, heating said foil composite in a vacuum whereby said foil composite melts and flows into said groove to form a continuous void-free metal mass in said groove, cooling said ceramic body and grinding any excess metal which extends out of said groove, said foil composite consisting of a plurality of metal foils including at least one layer of a metal foil selected from the group consisting of nickel, zirconium and manganese and at least one layer of a metal foil selected from the group consisting of Zirconium, titanium, molybdenum, vanadium, and copper.

2. A method as described in claim 1 wherein said groove is up to 0.010 inch wide and at least 0.002 inch deep.

3. A method as described in claim 1 wherein said metal foil composite is in the form of a titanium foil wrapped in a nickel foil.

4. A method as described in claim 1 wherein said ceramic body is an alumina body.

5. A method for filling a narrow groove in a ceramic body such as in a transducer assembly and the like with metal to form a continuous void-free metal strip comprising the steps of conditioning said body to provide a clean, dry groove in a degassed body, placing metal foil on said body whereby said foil completely covers the top of said groove, said metal foil consisting of zirconium foil wrapped in nickel foil, clamping said foil to said ceramic body with sufficient pressure to keep the foil from moving, heating said foil in a vacuum whereby said foil melts and flows into said groove to form a continuous void-free metal mass in said groove, cooling said ceramic body and grinding any excess metal which extends out of said groove.

6. A method as described in claim 5 wherein said metal foil consists of 2 layers of zirconium and 4 layers of nickel foil.

'7. A method as described in claim 5 wherein said metal foil contains 10 to 35% by weight nickel.

8. A method as described in claim 5 wherein said heating step is at a temperature between 950 C. and 1350" C.

References Cited UNITED STATES PATENTS 2,676,392 4/ 1954 Buhrendorf 29606 3,138,850 6/1964 Loro et al 29-620 X 3,246,384 4/1966 Vice 29603 3,287,161 11/1966 Schwertz et al. 3,332,145 7/ 1967 Klinkenberg.

JOHN F. CAMPBELL, Primary Examiner.

P. M. COHEN, Assistant Examiner. 

1. A METHOD FOR FILLING A NARROW GROOVE IN A CERAMIC BODY SUCH AS IN A TRANSDUCER ASSEMBLY AND THE LIKE WITH A METAL TO FORM A CONTINUOUS VOID-FREE METAL STRIP COMPRISING THE STEPS OF PLACING METAL FOIL COMPOSITE ON SAID BODY WHEREBY SAID FOIL COMPOSITE COMPLETELY COVERS THE TOP OF SAID GROOVE, CLAMPING SAID FOIL COMPOSITE TO SAID CERAMIC BODY WITH SUFFICIENT PRESSURE TO KEEP THE FOIL COMPOSITE FROM MOVING, HEATING SAID FOIL COMPOSITE IN A VACUUM WHEREBY SAID FOIL COMPOSITE MELTS AND FLOWS INTO SAID GROOVE TO FORM A CONTINUOUS VOID-FREE METAL MASS IN SAID GROOVE, COOLING SAID CERAMIC BODY AND GRINDING ANY EXCESS METAL WHICH EXTENDS OUT OF SAID GROOVE, SAID FOIL COMPOSITE CONSISTING OF A PLURALITY OF METAL FOILS INCLUDING AT LEAST ONE LAYER OF A METAL FOIL SELECTED FROM THE GROUP CONSISTING OF NICKEL, ZIRCONIUM AND MANGANESE AND AT LEAST ONE LAYER OF A METAL FOIL SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUM, TITANIUM, MOLYBDENUM, VANADIUM, AND COPPER. 